The present application relates generally to semiconductor device manufacture, and more specifically to the formation of FinFETs having electrically-isolated fins with different fin heights.
Fully-depleted devices such as fin field effect transistors (FinFETs) are candidates to enable scaling of next generation gate lengths to 14 nm and below. Fin field effect transistors (FinFETs) present a three-dimensional architecture where the transistor channel is raised above the surface of a semiconductor substrate, rather than locating the channel at or just below the surface. With a raised channel, the gate can be wrapped around the sides of the channel, which provides improved electrostatic control of the device.
The manufacture of FinFETs typically leverages a self-aligned process to produce extremely thin fins, e.g., 20 nm wide or less, on the surface of a substrate using selective-etching techniques. A gate structure is then deposited to contact multiple surfaces of each fin to form a multi-gate architecture.
The gate structure may be formed using a gate-first or a gate-last fabrication process. A gate-last process, such as a replacement metal gate (RMG) process, utilizes a sacrificial or dummy gate, which is replaced by a functional gate after device activation, i.e., after dopant implantation into source/drain regions of the fins and an associated drive-in anneal, in order to avoid exposing the functional gate materials to the thermal budget associated with activation.
Compared with fins that are contiguous with the substrate, Applicant has observed that dielectrically-isolated FinFETs exhibit superior electrostatic control without requiring extensive sub-fin punch-through stop doping. Such an isolated structure increases device variability and improves leakage characteristics.
Fins having different heights may be used to locally define the channel length of different devices on the same substrate. However, notwithstanding recent developments, it remains a challenge to form isolated semiconductor fins on the same substrate that also have different fin heights.